A) Field of the Invention
The present invention relates to an electronic circuit device and its manufacture method, and more particularly to an electronic circuit device having a countermeasure against a surge voltage and its manufacture method. The present invention relates also to a manufacture method for a varistor suitable for application to an electronic circuit device and to a manufacture method for a semiconductor device having a varistor.
B) Description of the Related Art
Malfunction caused by electrostatic surges and noises is becoming an important issue as a drive frequency of electronic components becomes high. Electronic components, typically dielectric filters and surface acoustic wave (SAW) filters having piezoelectric material, are likely to generate electrostatic surges because these components have piezoelectric effect that voltage is generated upon application of a stress.
In a high frequency device disclosed in JP-A-2004-72584, a varistor is mounted between an antenna terminal and a SAW filter to protect the electronic circuit from electrostatic surges. By mounting a varistor, it is possible to provide a countermeasure against electrostatic surges of an electronic circuit board on which a SAW filter is mounted.
Japanese Patent No. 2912081 discloses a varistor using a strontium titanate thin film. According to this invention disclosed in Japanese Patent No. 2912081, a titanium film is subjected to a hydrothermal process in aqueous solution containing strontium ions to form a strontium titanate film having high crystallinity.
An electronic circuit board having a SAW filter mounted thereon is provided with an electrostatic surge countermeasure by mounting a varistor. However, a SAW filter itself is not provided with the electrostatic surge countermeasure. Namely, a worker handling each component on the substrate is not provided with the electrostatic surge countermeasure. Therefore, the worker feels uncomfortable shocks of electrostatic surges in some cases.